On 16 July 2014, the club signed Joan Capdevila, a European Championship and World Cup winning defender with Spain, as its marquee player. He said: "India is a huge country and it should be a privilege for me to be a small part in popularizing this global game here and working with the young talented footballers of North East India".[4]

On 19 August the club hired its first manager, New Zealander Ricki Herbert, who had represented and managed his nation at World Cups.[5]

For their second season, NorthEast United signed former Portugal international Simão Sabrosa as their new marquee signing.[7] On 1 July 2015 the team announced their manager for the 2015 season, former Venezuela national coach, César Farías. The team lost all three of their opening matches with Simão absent through injury, but then earned a 2–0 home win over Chennaiyin FC in which the marquee player won and dispatched an added-time penalty kick to open the scoring.[8] The club entered the top-four for semi-finals by the end of the season but lost their position to Chennaiyin, who defeated Pune City to gain 3 points and secure the spot.

On 13 May 2016, NorthEast United announced Sérgio Farias as the club's new manager.[9] However, Sérgio Farias joined his former club Suphanburi FC for a second stint forcing NorthEast United to look for a new coach. On July 9, 2016, NorthEast United officially announced Sérgio Farias' exit.[10] On July 23, 2016, NorthEast United announced Nelo Vingada as the club's new manager.[11] The club again got a chance to enter the top-four for semi-finals if they defeat Kerala Blasters but lost and hence, losing their semi-final chance. The club scored 14 goals and conceded 14 goals in that season. More than half of the goals (8) were scored by the South American duo Nicholas Velez and Emiliano Alfaro with 3 and 5 goals respectively.

On 17 July 2017, in hope for a great season NorthEast United signed the young Portuguese manager Joao Carlos Pires de Deus.[12] After playing its preseason games in Antalya, Turkey. The team began its season against the ISL debutants Jamshedpur FC. The game ended in a draw with neither side managing to find the back of the net despite NorthEast playing against a 10 men Jamshedpur in the last 20 minutes.[13] Next they played Chennaiyin FC in Chennai, where they failed to keep the record of never losing in Chennai after losing 3–0.[14] NorthEast witnessed their first win of the season where they defeated Delhi Dynamos 0–2 in the opponent's ground. The first goal of the match came from Marcinho in the 17th minute, when a cross by Halicharan Narzary from the left flank found him unmarked inside the box. The second goal came from the striker Danilo in the 22nd minute, when he pressured the Delhi custodian Albino Gomes and made him make error inside his own box, leaving an open goal for Danilo to score his first and last goal of the season and, 500th goal of the league.[15] It was followed by a 4 match losing streak right after which the Portuguese manager was sacked.[16] The team management brought in the ex-Chelsea boss Avram Grant as a technical advisor who acted as a caretaker manager in the absence of Joao.[17] He was later promoted to Head Coach on 12 January 2018, after the team released an official statement about Joao's sacking.[18] The team won 2 out of the first 3 games under Grant, where they defeated FC Goa 2–1[19] and Chennaiyin FC 3–1[20] at home. Seiminlen Doungel scored the first ever hat-trick for NorthEast United in that match. The team failed to win a single match after that, ending the season in a long 8 match winless streak in which they drew 1 match and lost all other matches. They finished the season at the last position managing to win only 3 matches and scoring 12, which was the lowest for the season. Overall the team didn't perform well enough.
It was the worst performance in the season since the club came into existence

On 19 February 2018, AIFF announced the Indian Super Cup as a replacement for the Federation Cup. It will be played between 16 teams, the top 6 teams of ISL and I-League and the remaining 4 will be picked through a qualifier played between the bottom 4 from both league. NorthEast United participated in the Cup Qualifiers for the 4 remaining spots. NorthEast United played their qualifier match against Gokulam Kerala on 15 March 2018 which they lost 2–0 and got eliminated.

2018-19 is the fifth season of the club's existence. The season started with a positive start under coach Eelco Schatorrie with NorthEast United drawing with Goa and two consecutive wins over ATK and defending champions Chennaiyin. Against Chennaiyin, NorthEast United made a thrilling comeback after down 3-1 in 35th minute to 3-3 in first half and winning the match 4-3. After Some thrilling victories against Kerala Blasters and Chennaiyan the club strengthened its way to the playoffs. After playing 17 matches and getting 28 points Northeast United finally qualified for the playoffs with Jamshedpur losing a chance to the playoffs with a draw against Chennaiyan FC and also for Super Cup. They also lost the least number of matches and conceded the least number of the goals of any team in the league. They also made a club record of 29 points. Former Nigerian international Bartholomew Ogbeche became the highest goalscorer of the club scoring 12 goals. NorthEast United became a major force in the league. They defeated Bengaluru in the first leg of semi-finals with Mascia scoring in the dying moments in the game. Northeast United lost their second leg against Bengaluru which also saw Federico Gallego getting injured.

The crest of NorthEast United FC is featured with 8 stars at the top representing each state of North-east India. The crest is designed with red, black and white applications, with the club name written in bold letters between the main crest and the stars. The club changed the crest with an entirely gold crest for its third season of ISL. It was changed back to the original color after the end of the season. The original crest, and a red and white is currently in use by the club.

NorthEast United FC play their home matches at the Indira Gandhi Athletic Stadium, Guwahati. In 2014, to meet FIFA regulations, the stadium was renovated and its capacity was increased from 12,000 to 35,000. Indira Gandhi Athletic Stadium hosted the opening ceremony of ISL 2016. NorthEast had the highest attendance on 20 October 2016, when a record attendance of 32,844 turned up to witness the match between NorthEast United and Chennaiyin FC. The capacity was again reduced to 23,850 after the installation of bucket seats for the 2017 FIFA U-17 World Cup. The stadium saw the lowest attendance in the history of ISL when only 1,121 fans turned up to witness the match played between NorthEast United FC and Kerala Blasters FC on 17 February 2018.[21]

NorthEast United is owned by John Abraham, who is an Indian Bollywood actor, producer and former model.[22] It is the only ISL club that is not owned by any company or corporation. John Abraham is said to have spent money from his own pocket in order to finance the club.

The official supporters group or fan club of the club is the Highlander Brigade.[23][24]
The fan club can be traced back to its roots where it was merely a WhatsApp group formed out of a handful of followers of a Facebook page "NorthEast United FC Fans". They not only support NorthEast United but also support the Indian team.

Before the fourth season of the Indian Super League, keeping an eye on the occasion, a major chunk of the group members decided to meet and attempt to do something big. And under the tutelage of key members helming certain responsibilities, the Brigade grew and spread out rapidly.

With over 500 members stretched out across the 8 states of the Northeast India, The Highlander Brigade is strong and capable enough to indulge in "Travelling Fans" and hosting football-related events in the city.
To ensure that the football culture remains proactive in the city, the brigade plans to indulge in more fan activities in the future as well.

Even after a lackluster fourth season for the club, the Highlander Brigade could be seen cheering them on with the red-white-black flags and banners thumping down the beats in a raging winter cold under the lights.And therefore these beloved group of people were received fondly by the club and the players.

Highlander Brigade remains an excited bunch of people in a football crazy region and along with the other fan clubs of the country, they form a pivotal part of the umbrella of football culture as fans in India.

NorthEast United play the Eastern Derby or East Indian Derby against neighbouring club ATK. NorthEast United have won three matches, drawn two match and lost five matches till date against ATK. The two clubs represents two football crazy regions of India and also have a huge fan and supporter base.[27][28]